The present invention relates to a device that distributes a microwave signal in a waveguide between two waveguide branches.
For transfer of microwaves, transmission lines consisting of waveguides and different waveguide components are used. So called T-junctions are such components that are used when a microwave signal is to be split between two outputs. Cascade connections of several T-junctions make a distribution among more outputs possible.
In those cases in which the power is to be divided equally among the outputs, this is achieved with a symmetrical junction. In many cases however a non-uniform distribution is desired, for example the power at the outputs should differ 4 dB within a specified frequency range.
The division can occur either in the electrical field plane, i.e. the E-plane or in the magnetic field plane, i.e. the H-plane. Distribution via an E-plane junction is easily done by varying the size of the openings of the connected waveguides, in principle in proportion to the power that is to be guided to respective outputs. The dividing wall is perpendicular to the electrical field, and does not cause much disturbance of the field in the waveguide.
This is not as easily accomplished in the H-plane. A dividing wall becomes parallel with the electrical field in this case, and thus creates a considerable disturbance. Furthermore, it is the H-plane dimension, the so called a-measure (the width of the waveguide), that dictates the propagation constant in the waveguide. It has been shown in trials that the distribution relationship becomes frequency dependent, which in many applications cannot be accepted or in any case leads to deteriorated characteristics.
With these types of constructions there are also demands on matching of the "port" through which input of the microwave signal occurs, and also often demands of phase uniformity between the output ports. This can be accomplished with different impedance matching structures that are placed in the waveguides. An example of such an impedance matching structure can be found in the Japanese patent document JP55-14757. In this case the impedance matching structure is also used for distribution of the microwave signals in the junction. However, by using only a single structure it can be difficult to decide the power distribution as well as the matching, and at the same time achieve sufficiently wide bandwidth.